A slang term for the feminazis, people who are easily offended, hate men (especially those of Caucasian ethnicity), have no sense in basic human logic, believes in idiotic ideologies, and attacks all who oppose them, mostly by screeching senseless garbage and sometimes physically.
The name derives from the fact feminazis screech at everyone and everything they hate. While the beast part refers to their common practice of refusing to shave their body hair as they think it means their giving in to the concept of being attractive to men.